In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to increase the degree of integration in recent years.
In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been generally used. However, it is difficult to perform microfabrication with a line width of a sub-quarter micron level using near ultraviolet rays.
Therefore, in order to enable microfabrication with a line width of 0.20 μm or less, utilization of radiation with a shorter wavelength has been studied. Deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have gained attention.
As a radiation-sensitive resin composition applicable to the excimer laser radiation, a number of compositions utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter called “photoacid generator”) upon irradiation (hereinafter called “exposure”) have been proposed. Such a composition is hereinafter called a chemically-amplified radiation-sensitive composition.
As the chemically-amplified radiation-sensitive composition, JP-A-59-45439 discloses a composition comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group in the polymer by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which allows the exposed area on the resist film to be readily soluble in an alkaline developer.
Many conventional chemically-amplified radiation-sensitive compositions use a phenol resin as a base. If the composition contains such a resin, deep ultraviolet rays used as radiation for exposure are absorbed in the resin due to aromatic rings and cannot sufficiently reach the lower layers of the resist film. Because of this, the dose of the radiation is greater in the upper layers and is smaller in the lower layers of the resist film. This causes a resist pattern to be thinner in the upper portion but to be thicker toward the lower portion, thereby forming a trapezoid shape after development. No sufficient resolution can be obtained from such a resist film. If the resist pattern after development is in the shape of a trapezoid, desired dimensional accuracy cannot be achieved in a succeeding step such as an etching step or ion implantation step. Moreover, if the shape of the upper part of the resist pattern is not rectangular, the rate of removal of the resist by dry etching is increased, whereby it is difficult to control etching conditions.
The shape of the resist pattern can be improved by increasing the radiation transmittance of the resist film. For example, (meth)acrylate resins represented by polymethylmethacrylate are desirable from the viewpoint of radiation transmittance due to the superior transparency to deep ultraviolet rays. JP-A-4-226461 discloses a chemically-amplified radiation-sensitive resin composition using a methacrylate resin. However, this composition has insufficient dry etching resistance due to the absence of an aromatic ring, although the composition excels in microfabrication performance. Therefore, this composition also has difficulty in performing etching with high accuracy and cannot satisfy transparency to radiation and dry etching resistance at the same time.
A method of introducing an alicyclic ring into the resin component in the composition instead of an aromatic ring has been known as a means of improving dry etching resistance without impairing radiation transmittance of the resist made from a chemically-amplified radiation-sensitive resin composition. A chemically-amplified radiation-sensitive resin composition using a (meth)acrylate resin having an alicyclic ring is proposed in JP-A-7-234511, for example.
This composition, however, comprises groups which are comparatively easily dissociated by conventional acids (for example, an acetal functional group such as a tetrahydropyranyl group) and groups which are comparatively difficult to be dissociated by an acid (for example, a t-butyl functional group such as a t-butyl ester group, t-butylcarbonate group) as an acid-dissociable functional group in the resin component. The resin component having the former acid-dissociable functional group provides a resist with favorable basic properties, particularly excellent sensitivity and pattern formability, but the composition has a problem with storage stability. The resin component having the latter acid-dissociable functional group, on the other hand, provides a composition with good storage stability, but the resist has a problem with its basic properties, particularly with sensitivity and pattern formability. In addition, inclusion of an alicyclic structure in the resin components of this composition increases hydrophobicity of the resin, resulting in poor adhesion to substrates.
In view of recent progress in the microfabrication of semiconductor devices, development of a novel resin component exhibiting high transmittance of radiations, having excellent basic properties as a resist, and suitable for use in chemically-amplified radiation-sensitive compositions which can be adapted for short wavelength radiations represented by deep ultraviolet rays has been undertaken (for example, refer to JP-A-2002-72484). However, there have been no resin components satisfying all of these requirements.